High power transistors frequently occupy a major portion of the chip area in a power integrated circuit (IC). Vertical high power devices occupy less area than horizontal high power devices but need contacts to carry current from the buried drain or buried collector to the surface of the substrate. Typically a sinker contact is formed by implanting dopant at a series of different energies to form a highly doped diffusion column extending from the top surface of the substrate down to the buried drain or buried collector. Even with the sinker contact diffusion during operation when high current flows through the diffusion column a significant voltage drop may occur which can limit the performance of the vertical high power transistor.
Some devices on ICs require low contact resistance for improved performance. Typically to reduce contact resistance the diffusion area is increased and multiple contacts are formed to the diffusion. This increases the area of the IC and may also increase the diffusion capacitance which can degrade IC performance.